BEIRUT — A high-profile international mission to end the Syrian crisis stumbled Friday before it began as the opposition rejected calls by U.N. envoy Kofi Annan for dialogue with President Bashar Assad as pointless and out of touch after a year of violence.

The dispute exposes the widening gap between opposition leaders who say only military aid can stop Assad’s regime, and Western powers who fear more weapons will exacerbate the conflict.

As the prospects for diplomacy faltered, Turkey reported the defections of three high-ranking Syrian military officers — two generals and a colonel — as well as two sergeants, a significant development because until now most army defectors have been low-level conscripts.

A deputy oil minister also deserted Assad’s regime this week, making him the highest-ranking civilian official to join the opposition.

The White House welcomed the reported defections as a sign the regime is cracking from within and that Assad will eventually fall.

Western and Arab powers are backing Annan’s two-day trip to Syria, starting Saturday, when he is to meet with Assad. The former U.N. secretary-general — now a special U.N.-Arab League envoy for Syria — has said he seeks to start a “political process” to end the crisis and warned against further militarization of a conflict that appears headed toward civil war.

“I hope that no one is thinking very seriously of using force in this situation,” Annan said Thursday in Cairo. “I believe any further militarization would make the situation worse.” He said he would present “realistic” solutions, but did not elaborate.

Opposition leaders and activists rejected Annan’s plans Friday, saying they ignore the nature of Assad’s authoritarian regime as well as the thousands killed by security forces, many while peacefully calling for political reform.

By phone from Paris, the head of the Syrian National Council told The Associated Press that Annan was overlooking what the opposition considers the root of the problem: The regime’s use of overwhelming military force to crush dissent.

“Any political solution will not succeed if it is not accompanied by military pressure on the regime,” said Burhan Ghalioun. “As an international envoy, we hope (Annan) will have a mechanism for ending the violence.”

The Syrian National Council has called for foreign military intervention, believing it is the only way to stop Assad’s tanks and soldiers from firing on civilian areas. It recently formed a military office to try to coordinate efforts to bring in military aid for armed groups across the country who fight under the name of the Free Syrian Army.

Ghalioun said he worried Annan’s trip would stall more effective steps to stop the violence.

“My fear is that, like other international envoys before him, the aim is to waste a month or two of pointless mediation efforts,” he said.

Activists in Syria also said it was too late to talk.

“If the popular leaders inside Syria have decided that there can be no dialogue with the killer who is attacking us with tanks and rockets, how can he call for dialogue?” said an activist from the central city of Homs, who gave his name only as Abu Bakr for fear his family would be targeted. “You can’t negotiate with someone who has a gun to your head.”

Annan’s visit marks a new international push for peace nearly a year after protesters took to the streets to demand Assad’s ouster, inspired by Arab Spring uprisings in Tunisia and Egypt. Since then, the regime has dispatched snipers, tanks and civilian gunmen to crush dissent. As the death toll mounted, protests have spread, and some have taken up arms to defend themselves and attack government forces.

The conflict is now one of the bloodiest of the Arab Spring, with the U.N. saying more than 7,500 people have been killed. Activists put the number at more than 8,000.

So far, Western powers have declined to intervene. Unlike in Libya, where a U.N.-sanctioned bombing campaign helped rebels topple Moammar Gadhafi last year, Syria has key allies in Iran and the Lebanese militant group Hezbollah, and shares a border with the region’s closest American ally, Israel. Outright war in Syria could spark a regional conflagration.

On Friday, the U.N. humanitarian chief said the Syrian government had agreed to a joint mission to assess the country’s humanitarian needs — a rare concession by a regime that restricts work by outside groups.

Speaking in Turkey, Valerie Amos said the mission would be the first step toward setting up a longer-term system “which allows humanitarian organizations unhindered access to evacuate the wounded and deliver desperately needed supplies.”

She said she was waiting for the Syrian government’s response to a proposed plan.

Despite growing international condemnation, Assad’s regime has remained largely intact. The report of military defections on Thursday was a notable development because of their high ranks and because it came a day after a deputy oil minister turned against Assad.

The White House said the developments were encouraging.

“If the reports are true, it’s certainly a sign that there are significant cracks in the Assad regime,” and lend weight to the U.S. view that Assad will fall, said White House spokesman Josh Earnest. The defections “are a courageous step by members of the regime demonstrating their loyalty to and support for the Syrian people and their aspirations.”

Still, U.S. intelligence officials said the defections were not from Assad’s inner circle and there were no indications of the broader Syrian elite abandoning support for him, the best indication of a weakening of his regime. Signs of a worsening economy could be the biggest threat to Assad’s stability, with food prices doubling, refined fuel growing scarce and unemployment rising.

The defecting military officers were among more than 200 Syrians who have fled to refugee camps in Turkey since Thursday as the Syrian government appears to gear up for an assault on opposition areas in Idlib province along the border.

Reinforcements have been pouring into Idlib for days, including dozens of tanks and armored personnel carriers.

“Many people are fleeing the area, fearing military operations,” said Rami Abdul-Rahman of the Britain-based Syrian Observatory for Human Rights. Much of the buildup was in the mountainous Jabal al-Zawiya region and the town of Saraqeb.

The Observatory said 54 people were killed across Syria on Friday, almost half of them during government raids of villages in Idlib.

Ten people were killed by gun and mortar fire in Homs, and security forces shot dead others around the country during protests, the group said. Five more bodies were found in Homs’ Baba Amr neighborhood, which the government seized from rebels last week after weeks of siege and shelling.

Protesters took to the streets Friday to call on the Kurdish minority to join the uprising.

Kurds are Syria’s largest ethnic minority, making up 15 percent of the country’s 23 million people, and have long complained of neglect and discrimination. They have not joined anti-government protests in great numbers, but Assad apparently feared they would. Last year he granted citizenship to 250,000 Kurds who had been registered as aliens and barred from voting, owning property, attending state schools and holding government jobs.